Normally, in the prior art, when a CPU or other PU (central or other processing unit) is waiting upon some event external to the program, the operating system or an active program will run a poll loop where it will keep reading an event register, utilized by the PU in connection with the program, until the event that it is waiting upon occurs. While the program is operating the PU in polling the event register, the PU is not doing useful work. Typical modern processors often use virtual memory and the memory mapping of external devices for this communication. On the other hand, some processors, especially in a multiprocessor environment, only have access to local memory and not to virtual memory. Local memory is finite and, in typical multiprocessor configurations, no memory outside of this local memory can be accessed by load and store operations. Thus, the use of local memory for other PU functions is limited while awaiting response from an external device. If a PU is simultaneously awaiting communication responses from several devices, the available memory for other functions is even further limited.
Memory may also be used to keep track of whether or not there is valid data in an incoming or outgoing register. Valid data is data that has been placed in the register for use by a receiving device but has not yet been accessed by the receiving device.
It would thus be desirable to provide a mechanism for communicating with one or more external devices without burdening the local or even the virtual memory of a PU.
It would further be desirable to keep track of valid data without burdening receiving device memory.